Les Oxley wrote:
We are looking into running XFS on a 3TB FLASH MEMORY MODULE. We have a
question regarding the extent boundaries.
See the attached PowerPoint drawing, xfs.ppt We are running Linux.
Our media is 3 million contiguous 4KB blocks. We would like to define
an extent size of 1MB and this tracks the erasure block size
of the flash memory, and that greatly improves perfomance. We are trying
to understand where XFS places the extent boundaries with reference to
the contiguous block sequence.
Is this deterministic as indicated in the drawing ? That is, are the
extent boundaries on 256 block boundaries.
Any help would be greatly appreciated.
extents by definition land on filesystem block boundaries, and can in
general be any number of filesystem blocks, starting & ending most
anywhere on the block device.
If you wish to always allocate in 1m chunks, you might consider using
the xfs realtime subvolume, see the extsize description in the mkfs.xfs
man page. I'm not sure how much buffered IO to the realtime subvol has
been tested; pretty sure it works at this point, though the sgi guys
will correct me if I'm wrong... it's not exactly the normal mode of
Using the realtime subvol, however, all your file -metadata- will still
be allocated on the main data volume, in much smaller pieces.